Brian Comport, who has died aged 75, was the screenwriter for the cult films Mumsy, Nanny, Sonny and Girly (1970), The Fiend (1972) and The Asphyx (1973). Like so many others working in the British film industry during the last half century, he had ups and downs, but the horror feature films he wrote are widely regarded as classics of the genre.

His break into films came in 1967 when he was introduced to Norman Cohen, a film editor on his way to becoming a very successful director, who had acquired the film rights to Geoffrey Fletcher's 1962 book The London Nobody Knows. Cohen had secured James Mason to narrate the commentary and Brian was engaged to provide the words. It was Brian's idea to have Mason walk and talk directly to the camera, making the film a personal journey through scenes in some forgotten corners of "swinging London", an innovative format at that time. The film was a huge success as a second feature in cinemas, and has been re-released on DVD.

The youngest of four brothers, Brian grew up in and around Brixton and Streatham, south London, and was known as "Pesky". His father, William, was a journalist at Reuters, and from him Brian acquired a deep love of language. At primary school, though, he excelled only at football – he played once for Crystal Palace juniors – added to which, in his own words, he was "bone idle". At Dunraven secondary modern in Streatham, staff thought him bright and pressed him to move to the grammar school. Brian refused because he had found a teacher who could inspire him, Tony Hodgkinson. Hodgkinson would go on to be an expert in the field of film education, producing work for Unesco and teaching at several US universities. At the earliest opportunity Brian went to work as a messenger at the Rank Organisation, which at that time was the closest thing Britain had to a Hollywood "studio".

The London Nobody Knows, 1967, had James Mason, right, as the narrator. Photograph: Ronald Grant Archive

From Rank he went on to Reuters, working with the Czech wartime refugee Kurt Weisskopf, who encouraged his journalistic and creative writing skills. The mid-50s, when I first met Brian, was the era of the coffee bar and traditional jazz. He would sit in a corner of the Coffee Cabin on Streatham High Road, sketching poetry and clutching an LP of Dylan Thomas. The press dubbed some of the writers of the time "angry young men", and that characterisation suited Brian well. He adopted thick-rimmed spectacles and a submariner's thick polo-necked sweater bought from an army surplus store in Brixton market.

At a gathering in Notting Hill he met Maisie Mosco, already becoming established as a writer. After the success of The London Nobody Knows, Brian was commissioned in 1969 to adapt Mosco's play Happy Family into Mumsy, Nanny, Sonny and Girly for Freddie Francis, an Academy award-winning cinematographer who, as a director, had a reputation for making rather strange fantasy films. Mumsy, Nanny, Sonny and Girly is one of the most subtle of horror films, and distinctively British.

Then came Man of Violence (1971) for Pete Walker, an acclaimed director of low-budget exploitation films. Described as "an affectionate low-budget homage to the gangster thriller", it was recently re-released by the BFI on its Flipside label. In 1971 Brian wrote the original story and screenplay The Fiend, for the director Robert Hartford-Davis. Unashamedly warped, and starring the redoubtable actors Ann Todd and Patrick Magee, the film melded gospel and popular music in a way that was then very new. It dwelt on some of Brian's own preoccupations: the lead character has an Oedipus complex; and the vicar is crucified in his own church.

The Asphyx, Brian's favourite among his films, was directed by Peter Newbrook and starred Robert Stephens, Jane Lapotaire and Robert Powell. In 1972, in a change of direction into musical theatre, Brian wrote the book for Pull Both Ends, a musical set in a Christmas cracker factory, with music and lyrics by John Schroeder and Anthony King. Starring Gerry Marsden, of Gerry and the Pacemakers, it ran for 36 performances at the Piccadilly theatre. This was not a happy experience for Brian, who was unused to working with so many collaborators. After that, he wrote a very personal play, Plat du Jour (1973), for the Traverse theatre in Edinburgh, about a love triangle.

There followed a long period of unrealised projects, scripts for unproduced films, and pretty relentless disappointment, until in 1984 Brian left London for Australia. There he worked in journalism and was commissioned to write documentaries and corporate videos. The work was sporadic and poorly paid. When he developed cancer and other health problems, he decided in 1998 to return to London, where he lived in a beautiful almshouse in Brixton.

There he worked on a funny, insightful and moving memoir, The Mackerel Handshake, yet to be published. Despite increasing ill-health, he continued to demonstrate an acute sense of the ridiculous and a dexterity with words and ideas, combined with warmth and personal charm.

Brian married and divorced four times. He is survived by his children, Tom and Lucy.

• Brian Comport, screenwriter, born 16 April 1938; died 5 September 2013